1. Field of Invention
The present invention relates to a method of crystallizing an amorphous silicon layer and a crystallizing apparatus thereof in which the amorphous silicon layer is crystallized by using plasma.
2. Discussion of Related Art
In view of performance, low temperature polysilicon, of which product cost is low owing to its low formation temperature and which also provides wide image area, is as good as high temperature polysilicon. There are various methods for forming low temperature polysilicon, such as solid phase crystallization, laser crystallization and the like.
When providing low temperature crystallization under 400° C., which is disclosed in Hiroyaki Kuriyama, et al., Jpn. J. Appl. Phys., 31, 4550 (1992), the laser crystallization fails to provide uniform crystallization and has difficulty in forming polysilicon on a substrate having a wide area due to an expensive apparatus and low productivity.
When polysilicon is formed by solid phase crystallization, uniform crystals are provided by using an inexpensive apparatus. However, the solid phase crystallization requires high temperature and long crystallization processing time. Such process is seldomly applied to forming polysilicon on a glass substrate and has low productivity.
A new method of crystallizing amorphous silicon at low temperature, known as metal-induced crystallization, is disclosed in M. S. Haque, et al., J. Appl. Phys., 79, 7529 (1996). The metal-induced crystallization crystallizes amorphous silicon by contacting amorphous silicon with a specific kind of metal which induces crystallization of silicon and then by carrying out annealing, enabling lower crystallization temperature.
In Ni-induced crystallization, crystallization is accelerated by NiSi2 which is the last phase of Ni silicide and works as a crystal nucleus, which is disclosed in C. Hayzelden, et al., Appl. Phys. Lett., 60, 225 (1992). As a matter of fact, NiSi2, which has a lattice constant of 5.406 Å similar to 5.430 Å of silicon, has the same structure as silicon. Thus, NiSi2 works as a crystal nucleus of amorphous silicon, accelerating crystallization to the direction <111>, disclosed in Tanemasa Asano, et al., Jpn. J. Appl. Phys., Vol. 36, pp. 1415–1419 (1997).
The metal-induced crystallization is affected by annealing time and temperature as well as quantity of metal. The crystallization time generally decreases as the quantity of metal increases.
Metal-induced crystallization has a crystallization temperature, but unfortunately requires a long thermal processing time of over 20 hours at 500° C. Therefore, this method still requires a high crystallization temperature as well as a long thermal process time.
As the quantity of metal increases, the metal-induced crystallization becomes more effective. However, intrinsic characteristics of a silicon layer are changed due to metal contamination in the crystallized silicon layer.
Generally, if the metal layer is formed on the amorphous silicon layer by using the sputtering method, it is difficult to reduce the amount of the metal material in the crystallized silicon layer. If the metal layer is formed on the amorphous silicon layer by using the coating method, it is possible to reduce the amount of the metal material applied to the crystallized silicon layer. However, the problem of the metal contamination could not be effectively solved.
Accordingly, when metal-induced crystallization is used, an improved method is required which reduces thermal treatment time, crystallization temperature, and metal contamination in a film.